ANS (4.1)

Unit 2 Start

ANS influences a person’s ability to…

• Stay alert and regulated

• Respond to stress or threat

• tolerate sensory input

• participate in sleep, eating, toileting, mobility, social interaction, and therapy

Connect body state with occupational performance

ANS Feedback loop:

1. Detect changes

2. Send sensory info to CNS

3. Process info to spinal cord and brain

4. Respond through autonomic motor output

5. Adjust organs, glands, blood vessels, and smooth/cardiac muscle

ANS system contains:

• Afferent pathways: sensory info to CNS

• Central processing: integration in spinal cord, brainstem, etc

• Efferent pathways: motor output from CNS to organs, glands vessels, and muscle

Types of receptors in ANS:

Mechanoreceptors

Chemoreceptors

Nociceptors

Thermoreceptors

Mechanoreceptors detect…

Stretch or pressure

• ex: Blood pressure, bladder fullness

Chemoreceptors detect…

Blood chemistry

• ex: Oxygen, CO_2, pH

Nociceptors detect…

Tissue threat or damage

• ex: visceral pain

Thermoreceptors detect…

Temperature

• ex: body temperature regulation

Information from receptors enter the CNS through these 2 routes…

1. Into the spinal cord via dorsal rots

2. Into the brainstem via cranial nerves

What does medulla help to regulate?

• HR

• BP

• Respiration

• Vasoconstriction/Vasodilation

What do pons regulate?

Breathing

How can hypothalamus affect the ANS?

Major regulator of homeostasis and internal body balance

How can thalamus affect the ANS?

Relays information that can contribute to awareness and emotional meaning

How can Emotion/motivation systems affect the ANS?

Can trigger autonomic responses such as increased HR, sweating, blushing, crying or changes in breathing

When a person feels anxious.. they can feel

• Increased HR

• Faster or shallow breathing

• Sweating

• Dry mouth

• Muscle tension

• Sweating

Most autonomic efferent pathway uses 2 neuron pathway

1. Preganglionic neuron: cell body in CNS that travels to autonomic ganglion

2. Postganglionic neuron: axon travels to organ

Preganglionic neuron > Postganglionic neuron > Organ

ANS pathway summary

Usually involuntary, 2-neuron chain

• Smooth muscle, cardiac muscle, glands

• Internal regulation and homeostasis

Chemical messengers within ANS:

• Acetylcholine

• Norepinephrine

• Epinephrine

Preganglionic sympathetic neurons located:

Spinal cord T1-L2

Parasympathetic preganglionic neurons arise from:

Brainstem through cranial nerves

Sacral spinal cord S2-S4

Parasympathetic ganglia is located:

near or on target organs

Vagus nerve carries parasympathetic fibers to what organs:

Heart, Lungs, Digestive system

Vagal activity can contribute to…

• Slower HR

• Bronchial constriction

• Increased digestive activity

• Increased glandular secretions

Enteric division regulations in the GI:

• Motility

• Secretions

• Blood flow in the gut

• Sphincter activity

Enteric division is influenced by:

Sympathetic activity

Parasympathetic activity

3 Types of Autonomic responses:

Fight/Flight: prepares the body for action

Freeze: catatonic (can’t move or speak)

• Heightened vigilance

• Reduced movement

• Slowed HR

Orthostatic hypotension is defined as:

A drop of at least 20 mmHg systolic OR 10 mmHg diastolic BP within the first 3 minutes of standing

Orthostatic hypotension mechanism:

Gravity causes blood to pool in the lower body, which can reduce venous return, cardiac output, arterial pressure, blood flow to brain

Orthostatic hypotension symptoms:

• Dizziness, light-headed

• feeling faint

• weakness or fatigue

• Nausea

• Blurred vision

• Fainting/syncope (passing out)

Spinal cord lesion autonomic effect…

Interrupt autonomic control below lesion: can affect BP, sweating, bowel/bladder, sexual function, and temperature regulation

High spinal cord or brainstem lesion autonomic effect…

May affect breathing, HR, BP, and other life-sustaining functions

Hypothalamus lesion autonomic effect…

May disrupt homeostasis, temperature regulation, appetite/metabolism, and emotional/autonomic responses